\name{Zpg}
\alias{Zpg}
\alias{as.Zpg}
\alias{as.Zpg.Arma}
\alias{as.Zpg.Ma}
\alias{as.Zpg.Zpg}
\title{ Zero-pole-gain model }
\description{
  Zero-pole-gain model of an ARMA filter.
}
\usage{
Zpg(zero, pole, gain)

\method{as.Zpg}{Arma}(x, ...)

\method{as.Zpg}{Ma}(x, ...)

\method{as.Zpg}{Zpg}(x, ...)

}
%- maybe also 'usage' for other objects documented here.
\arguments{
  \item{zero }{complex vector of the zeros of the model.}
  \item{pole }{complex vector of the poles of the model.}
  \item{gain }{gain of the model.}
  \item{x }{model to be converted.}
  \item{\ldots}{ additional arguments (ignored). }
}
\details{
  \code{as.Zpg} converts from other forms, including \code{Arma} and \code{Ma}. 
}
\value{
  An object of class "Zpg", containing the list elements:
  \item{zero }{complex vector of the zeros of the model.}
  \item{pole }{complex vector of the poles of the model.}
  \item{gain }{gain of the model.}
}
\author{ Tom Short }
\seealso{ \code{\link{Arma}}, \code{\link{bilinear}} }
\keyword{ math }
